For example, with a semiconductor light emitting device of the blue type, as there is shown a schematic diagram of one example of the light emitting chip thereof (hereinafter, referred to as "LED chip") in FIG. 4, on an insulating substrate 21 made of sapphire, are laminated an n-type layer (cladding layer) 23 obtained by epitaxially growing, for example, an n-type GaN; an active layer 24 made of materials having smaller bandgap energy than that of the cladding layer, for example, an InGaN based (which denotes that the ratio of In to Ga is capable of changing variously, and the same shall apply hereinafter) compound semiconductor; and a p-type layer (cladding layer) 25 made of a p-type GaN. Then, the surface thereof is provided with a p-side electrode 28 so as to be electrically connected to the p-type layer 25 via a diffused metal layer (not shown). An n-side electrode 29 is provided so as to be electrically connected to the n-type layer 23 exposed by etching a part of the laminated semiconductor layers, thereby forming a LED chip.
With this kind of semiconductor light emitting device, the carrier concentrations are set as to be optimized in terms of the carrier confinement effect on the active layer 24 for the n-type layer 23 and the p-type layer 25 sandwiching the active layer 24. For example, the n-type layer 23 is formed with a constant carrier concentration of the order of 10.sup.18 cm.sup.-3.
As described above, in a conventional semiconductor light emitting device using gallium nitride based compound semiconductor, the carrier concentration of the n-type layer is set at an optimum level for emitting characteristics, and the n-type layer is formed with a uniform carrier concentration from top to bottom thereof. Then, an n-side electrode is provided so as to be in contact with a part of the n-type layer exposed by etching. However, the larger the carrier concentration of the n-type layer on which the n-side electrode is provided is, the more preferable it is for obtaining an ohmic contact with the electrode. It is preferable to be the order of 1.times.10.sup.9 cm.sup.-3, or more. Therefore, if the electrode is formed on the semiconductor layer with a carrier concentration limited from the emitting characteristics as described above, sufficient ohmic contact cannot be obtained, which results in a contributing factor in an increase in forward voltage.
In a conventional semiconductor light emitting device made of, for example, AlGaInP based compound semiconductor, or the like, a semiconductor laminated portion is provided so as to form an emitting layer on a semiconductor substrate. Accordingly, an n-type layer is connected to the semiconductor substrate with a high carrier concentration to provide an electrode on the semiconductor substrate. Therefore, even if the n-type layer is formed in accordance with the optimum carrier concentration for emitting characteristics, no problem will occur. However, the gallium nitride based compound semiconductor is laminated onto a sapphire substrate, and hence the electrode is provided directly on the n-type layer. This entails a problem that an ohmic contact cannot be obtained sufficiently. Further, there is also a disadvantage in that materials for an electrode are limited and covers a limited range of selection thereof in order to ensure a good ohmic contact even a bit in the state where it is difficult to obtain a good ohmic contact.